Choose a backup disk and set encryption options on Mac
Turn on Time Machine, add a backup disk or change to a different one, or adjust other settings.
Note: You may want to set up Time Machine in the evening so that the initial backup can be done overnight. If you back up to a Time Capsule or AirPort Extreme (802.11ac), the initial backup may be faster if your Mac is in the same room as the Time Capsule or AirPort Extreme (802.11ac), or if you connect your Mac to one of the Ethernet ports on the Time Capsule or AirPort Extreme (802.11ac). Subsequent backups take less time.
On your Mac, choose Apple menu
> System Preferences, then click Time Machine.Click Select Backup Disk, Select Disk or Add or Remove Backup Disk.
The options you see depend on whether you have one or more backup disks already set up.
Choose a disk from the list of backup disks and available disks.
Time Machine can’t back up to iPod or a disk formatted for Windows. If you connect a disk formatted for Windows, it can be reformatted (permanently removing all data) to a Mac filesystem format and used as a backup disk.
For increased security, select “Encrypt backups.”
Encryption is not available if you are using a disk directly connected to your Mac that is formatted using an Apple Partition Map (APM) or Master Boot Record (MBR) partition and the disk has more than one partition.
If the tick box is dimmed, hold your pointer over it for a moment to see an explanation; for example, the selected disk may need to be reformatted or repartitioned. If no explanation appears, the selected disk doesn’t support encryption.
Click Use Disk.
If you already set up one other disk, click Replace [disk name] or Use Both.
If you already have multiple backup disks, you don’t see this option.
If you’re asked to reformat the disk, either reformat the disk or choose a different disk.
Important: Reformatting erases all files on the disk, so do it only if you no longer need the files or have copied them to a different disk.
If you selected “Encrypt backups” (in step 4), type a password for the backup disk.
You may need to provide the password when you connect the disk to your Mac, or when you disconnect the disk or restart your Mac.
If you previously used a Time Capsule or networked disk for unencrypted backups and want to turn on encryption now, Time Machine must first erase the unencrypted backup before starting an encrypted backup.
To use multiple backup disks, repeat these steps for each disk.
Time Machine works best if you use your backup disk only for Time Machine backups. If you keep files on your backup disk, Time Machine won’t back up those files, and the space available for Time Machine backups is reduced.